1. Field of the Invention
The present invention relates to a light emitting unit on which a light emitting device such as an LED is mounted.
2. Description of the Related Art
Heretofore, it has been suggested that an LED as a light emitting device should be incorporated in an endoscope. For example, it is suggested that the LED should be arranged in an operating section of the endoscope and illuminative light from the LED should be guided to an endoscope distal end portion by a light guide to irradiate, whereby the subject is illuminated. In such a system, however, a light quantity is largely lost while the illuminative light passes through the light guide, and hence the sufficient light quantity cannot be obtained.
To obtain the sufficient light quantity, it can be contrived that an LED package is incorporated in the endoscope distal end portion. However, in the LED package of the large light quantity, a current of several hundred milliamperes or more needs to flow through the LED in order to obtain the large light quantity, and a comparatively large amount of heat is generated in the LED. In the large light quantity LED package, a heat release mechanism for releasing the thus generated heat is required, and hence a diameter of the package increases. Therefore, when the conventional large light quantity LED package is used in the endoscope distal end portion, a diameter of the endoscope distal end portion increases.
Moreover, the conventional large light quantity LED package has a configuration wherein the package is mounted in a face-up manner and subjected to wire bonding, or a configuration wherein the package is mounted on a silicon substrate or a sub-mount device in a face-down manner to connect electrodes from the sub-mount substrate to a lead frame via the wire bonding. In such a configuration, however, the heat generated in the LED cannot be efficiently released. Therefore, in the case where the conventional large light quantity LED package is used in the endoscope distal end portion, there become problems that the light quantity decreases, noise of an image pickup device increases, and the endoscope distal end portion becomes hot, through the heat generation.
An endoscope disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-24276 includes at least one light emitting device as an illuminative light source, and a printed wiring board on which this light emitting device is mounted and which is arranged at a distal end of an insertion portion of the endoscope. In the surface of the printed wiring board, a ground conductor pattern is formed by an area excluding areas occupied by signal conductor patterns except a ground conductor pattern and insulating areas.